Issue in Honor of Prof. B. S. Thyagarajan ARKIVOC 2001 (xi) 41-48
Unexpected reactions of organozinc reagents with Nacylbenzotriazoles
Alan R. Katritzky*, Olga V. Denisko, Yunfeng Fang, Lianhao Zhang, and Zuoquan Wang
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA E-mail:
[email protected]
This manuscript is dedicated to Prof. B. S. Thyagarajan (received 11 Sep 01; accepted 10 Feb 02; published on the web 18 Feb 02)
Abstract
Coupling N-acylbenzotriazoles with aliphatic and benzylic organozinc reagents in the presence of zinc bromide / Pd(II) catalyst (or zinc bromide / Ni(0) catalyst) did not result in formation of the expected ketones, but instead gave the corresponding carboxylic acid esters. This reaction apparently occurs by the insertion of oxygen dissolved in the solvent into the organozinc compound.
Keywords: N-Acylbenzotriazoles, organozinc reagents, oxygen insertion
Introduction
The transformation of carboxylic acid derivatives 1 into the corresponding ketones 2 (Scheme 1), avoiding over-reaction to tertiary alcohols 3, is important and much studied. Acyl chlorides, esters and amides have all been utilized. Selective conversions of acyl chlorides into the corresponding ketones have been studied with a wide variety of organometallics, including Grignards (Fe3+ catalysis),1 organoboron (Pd0 catalysis),2 organonickel,3 organozinc (Pd2+ catalysis),4 organotin (Pd catalysis),5 and organomercury (Pd0 catalysis)6 reagents (a comprehensive review on such reactions has recently been published7).
Scheme 1
The high reactivity of acyl halides and their incompatibility with acid-sensitive functionalities have driven efforts to find alternative solutions, with the major emphasis on amides. N,N-Dialkylamides with alkyl-, aryl-8 or vinyl-9 lithium and Grignard10 reagents afford
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